Behave WG J. Korhonen
Internet-Draft Nokia Siemens Networks
Intended status: Standards Track T. Savolainen, Ed.
Expires: January 2, 2011 Nokia
July 1, 2010
EDNS0 Flags Indicating AAAA Record Synthesis and Format
draft-korhonen-edns0-synthesis-flag-00.txt
Abstract
Advanced hosts and applications benefit of the knowledge of an IPv6
address, AAAA record, and a possible synthesis taking place in the
network. This specification defines ENDS0 flag bits for
communicating whether the synthesis is taking place, what is the used
IPv6 address format, and the IPv6 prefix and suffix used by the
DNS64. The communicated information enables hosts to perform a local
IPv6 address synthesis and to extract the IPv4 address out of the
synthesized IPv6 address.
Status of this Memo
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Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements and Terminology . . . . . . . . . . . . . . . . . 3
3. EDNS0 flags for indicating address synthesis . . . . . . . . . 3
4. Host behavior . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
As the networks transition to IPv6, connectivity to IPv4-only domains
has to be provided. NAT64 [I-D.ietf-behave-v6v4-xlate-stateful] and
DNS64 [I-D.ietf-behave-dns64] technologies can be utilized to make
IPv4-only peers look like being reachable over IPv6. The DNS64
utilizes IPv6 address synthesis to create local IPv6 presentations of
peers having only IPv4 addresses. Applications utilizing DNS for
resolving peers' IPv6 addresses can work seamlessly through protocol
translation taking place at NAT64.
The DNS64 cannot serve applications that are not using DNS, such as
those receiving and using IPv4 address referrals. Such applications
could nevertheless be able to work through NAT64, provided they are
able to create locally valid IPv6 presentations of peers' IPv4
addresses.
This specification describes a method for advanced applications to
learn the information required for a local IPv6 address synthesis.
The knowledge of IPv6 address synthesizing taking place may also be
useful if DNS64 is present in a dual-stack network access. In such
cases hosts may choose to use IPv4 addresses instead of synthesized
IPv6 addresses, and hence avoid traversal through NAT64.
2. Requirements and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. EDNS0 flags for indicating address synthesis
The mechanism for informing AAAA record synthesis taking place and
the used addressing format is using three bits of the ENDS0 OPT
header in the DNS response. The bits are structured as follows:
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+0 (MSB) +1 (LSB)
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0: | EXTENDED-RCODE | VERSION |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
2: |DO| SY | Z |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Possible values for SY-bits are:
000 reserved
001 prefix length /32
010 prefix length /40
011 prefix length /48
100 prefix length /56
101 prefix length /64
110 prefix length /96
111 address is not synthesized
Figure 1
The prefix length corresponds to the address formats documented in
"IPv6 Addressing of IPv4/IPv6 Translators document"
[I-D.ietf-behave-address-format] section 2.2.
The absence of the EDNS0 option means that either no synthesis took
place or the DNS64 does not support this specification. Either way,
when the EDNS0 option is missing, the host cannot conclude for
certain whether the AAAA response was synthesized or not. However,
if the host knows the name it asked for cannot have a real AAAA
record, it MAY search for the IPv4 address inside the received IPv6
address, and if found then make an educated guess of the address
format used by the DNS64. The host MAY learn the IPv4 address via an
A query, or have the address preconfigured.
[Editor's note: currently using extended flags has the least on-wire
overhead. However, it also allocates multiple scarce flag bits.
Therefore, the use of extended OPTION-CODE could be an alternative
approach.]
4. Host behavior
A host requiring information for a local IPv6 address synthesis or
NAT64 avoidance SHALL send a DNS query for an AAAA record of a well-
known IPv4-only fully qualified domain name (e.g. ip4.example.com)
[editor's note: whether this domain name must be reserved by IANA is
to be decided]. This may happen, for example, at the moment the host
is configured an IPv6 address of a DNS server. This may also happen
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at the time first DNS query for AAAA record is initiated.
If a host receives a negative reply, it learns there is no NAT64 in
the network. If the host receives AAAA reply, it knows the network
is utilizing IPv6 address synthesis. If the received IPv6 address
has a well-known prefix, the host can use that information for a
local IPv6 address synthesis. If the prefix is not well-known, the
host reads the ENDS0 flag values to learn the used address format.
Using the learned prefix length information, the host extracts from
the received IPv6 address the information used by the network for
IPv6 address synthesis (prefix, suffix, u-bit).
The information required for a local IPv6 address synthesis SHOULD be
made available for applications to utilize.
5. Security Considerations
No security considerations have been identified.
6. IANA Considerations
EDNS0 RFC 2671 [RFC2671] defines 16 bit extended flag field in the
OPT RR. These bits are encoded into the TTL field of the OPT record
(see Section 4.6 of RFC 2671).
This specification reserves three of extended flag bits as the SY-
bits. It is requested that the next available consequent leftmost
bits are allocated.
7. Acknowledgements
The authors would like to acknowledge Andrew Sullivan for presenting
general idea of ENDS0 option and SY-bit in Behave WG mailing list.
8. Normative References
[I-D.ietf-behave-address-format]
Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators",
draft-ietf-behave-address-format-08 (work in progress),
May 2010.
[I-D.ietf-behave-dns64]
Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum,
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"DNS64: DNS extensions for Network Address Translation
from IPv6 Clients to IPv4 Servers",
draft-ietf-behave-dns64-09 (work in progress), March 2010.
[I-D.ietf-behave-v6v4-xlate-stateful]
Bagnulo, M., Matthews, P., and I. Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers",
draft-ietf-behave-v6v4-xlate-stateful-11 (work in
progress), March 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
RFC 2671, August 1999.
Authors' Addresses
Jouni Korhonen
Nokia Siemens Networks
Linnoitustie 6
FI-02600 Espoo
Finland
Email: jouni.nospam@gmail.com
Teemu Savolainen (editor)
Nokia
Hermiankatu 12 D
FI-33720 Tampere
Finland
Email: teemu.savolainen@nokia.com
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